1. Field of the Invention
The present invention relates to wireless telecommunications. More particularly, the present invention relates to a novel and efficient smart antenna for a code division multiple access wireless communications system. If the smart antenna in the invention is employed at a base station and a desired mobile user moves around high rise buildings, the smart antenna would work more effectively than other existing smart antennas.
2. Description of the Related Art
In a third generation (3G) wireless communications system, particularly those specified in the wide band (W)-CDMA or the CDMA2000 standard, a base station has an option to employ a smart antenna technology. A smart antenna can suppress interfering signals of different DOAs from the desired users by using spatial diversity. Smart antenna technologies attract much attention these days as they support more users with a high quality of service and high data rates, up to 1.92 mega bits per second (Mbps). Efficient smart antenna schemes have appeared recently. One of them was invented by the present inventors and is in pending U.S. provisional patent application Ser. No. 60/164,552. It would be reasonable to include more realistic environments that have not been considered in the existing literature or inventions.
For example, when a mobile user moves around in a downtown of a city with high rise dense buildings, the direction of arrival angles (DOA) from the desired mobile user""s multipath signals may change abruptly at a base station receiver due to local scatters around the mobile user. This phenomena is called xe2x80x9cedge effects.xe2x80x9d One of the roles of a smart antenna at a base station is to track the DOAs of dominant multipath signals. The convergence speed of smart antenna weighting coefficients and the DOA tracking capability are critical issues in the design of smart antennas, especially when these edge effects occur frequently. Most of the existing literature or inventions concerning smart antennas do not include these edge effects, and a constant convergence parameter traditionally has been employed. There is still a need for a smart antenna with a fast convergence speed as well as a small mean square error (MSE) under an edge effect environment. Some of the existing literature, e.g., normalized least mean square (NLMS), have considered a time varying adaptive convergence parameter. Also, U.S. Pat. No. 5,999,800, Choi, has employed a time varying LaGrange multiplier. However, these existing literature or inventions have employed different optimization criteria or different adaptive schemes from the present invention.
A smart antenna that is a blind adaptive antenna array, is a method and system to suppress the multiple access interference and to improve performance of a wireless communications system, including CDMA such as third generation (3G) CDMA2000 and W-CDMA. A parameter is employed in a smart antenna processor. In general, a constant convergence parameter value is empirically determined and used after studying the convergence speed and the steady state MSE or other performance, such as a bit error rate. As the convergence parameter value increases, the convergence speed also increases but the MSE unfortunately increases and vice versa. The smart antenna with a constant convergence parameter would yield poor performance when the channel environment changes, which is true since a mobile user moves around in general. In the present invention, the convergence parameter value is adaptively changed and employed in a smart antenna processor. Two exemplary methods to update the convergence parameter are described. By employing such an adaptive convergence parameter value, the convergence speed can be increased and the steady state MSE can be decreased. Simulation test results confirm that a smart antenna using the adaptive convergence parameter schemes in the present invention shows improved performance for a CDMA system operating under a time-varying fading channel and the edge effects, compared to the existing schemes. In addition, the smart antennas according to the present invention have smaller computation loads than a competitive invention, such as Choi.
In accordance with the invention, there is provided a method of receiving a signal for use in combination with wireless communications. The invention includes the step of receiving a signal in multiple antennas. The received signal is processed utilizing an adaptive convergence parameter. According to one embodiment of the invention, the antennas are a multiple antenna array. According to another embodiment of the invention, the antennas are multiple antennas.
In accordance with one embodiment of the invention, the received signal is processed according to                               μ          ⁡                      (            k            )                          =                              γ            -                                                                                w                    _                                    H                                ⁡                                  (                  k                  )                                            ⁢                              xe2x80x83                            ⁢                                                R                  yy                                ⁡                                  (                  k                  )                                            ⁢                                                w                  _                                ⁡                                  (                  k                  )                                                                                        γ              2                        +                                                                                w                    _                                    H                                ⁡                                  (                  k                  )                                            ⁢                              xe2x80x83                            ⁢                                                R                  yy                  2                                ⁡                                  (                  k                  )                                            ⁢                                                w                  _                                ⁡                                  (                  k                  )                                                      -                          2              ⁢              γ                        -                                                                                w                    _                                    H                                ⁡                                  (                  k                  )                                            ⁢                              xe2x80x83                            ⁢                                                R                  yy                                ⁡                                  (                  k                  )                                            ⁢                                                w                  _                                ⁡                                  (                  k                  )                                                                                            =                                            γ              -                                                "LeftBracketingBar"                                      z                    ⁡                                          (                      k                      )                                                        "RightBracketingBar"                                2                                                                    γ                2                            +                                                                    "LeftBracketingBar"                                          z                      ⁡                                              (                        k                        )                                                              "RightBracketingBar"                                    2                                ⁢                                                      "LeftDoubleBracketingBar"                                                                  y                        _                                            ⁡                                              (                        k                        )                                                              "RightDoubleBracketingBar"                                    2                                            -                              2                ⁢                γ                ⁢                                                      "LeftBracketingBar"                                          z                      ⁡                                              (                        k                        )                                                              "RightBracketingBar"                                    2                                                              .                    
In accordance with an alternate embodiment, the signal is processed according to       μ    ⁡          (      k      )        =            1              γ        +                                            w              _                        ⁡                          (              k              )                                ⁢                      xe2x80x83                    ⁢                                    R              yy                        ⁡                          (              k              )                                ⁢                                    w              _                        ⁡                          (              k              )                                            =                  1                  γ          +                                    "LeftBracketingBar"                              z                ⁡                                  (                  k                  )                                            "RightBracketingBar"                        2                              .      
However, the invention is not limited to these two specific algorithms, which are exemplary.
The step of processing includes estimating a direction of arrival angle for antennas, the direction of arrival angle being separate from other signal data. Also included is the step of determining a better weighting coefficient.
In accordance with one alternative, the direction of arrival angle is utilized in forward link transmission. In accordance with another alternative, the direction of arrival angle is utilized in reverse link transmission. Other alternatives include that the antennas are in a base station, or are in a mobile station.
In accordance with the invention, there is further provided a system of receiving a signal for use in combination with wireless communications. The system includes at least one signal processor, responsive to a signal received in more than one antenna, having an adaptive convergence parameter. Optionally, the system includes a transmitter connected to the signal processor. Optionally, the system includes a receiver connected to the signal processor. Optionally, the antennas include multiple antennas. Optionally, the signal processor includes a filter, the filter having the adaptive convergence parameter.
Optionally, the signal processor includes a measurement of a direction of arrival angle for antennas, the measured direction of arrival angle being separate from other signal data. Alternatively, the signal processor further includes a determination of a better weighting coefficient. Alternatively, the measured direction of arrival angle has been obtained from a reverse link transmission.
According to one embodiment, the system includes a base station, wherein the antennas are in the base station. According to another embodiment, the system includes a mobile station, wherein the antennas are in the mobile station.
These and other objects, features and advantages of the present invention are readily apparent from the following drawings and detailed description.